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Growin’ Green

Mid-Summer Is Time For Tomato Blues

By Brent Gray

Growing your own food, especially tomatoes, is a very rewarding experience. It does not come without the usual headaches, however.   Here are a few problems for you to be on the look-out for while growing tomatoes this summer.
Blossom-end rot is a physiological disorder caused by a lack of calcium in the blossom end (bottom) of the fruit. It results in brown or tan areas on the blossom end.  These areas start as small lesions and gradually develop to cover nearly the entire bottom of the fruit. Although caused by a lack of calcium, it is actually a consistent lack of water that is most often responsible for its development. Since plants need more water during the hottest part of summer, this is when we see it most often.
White core is when tomatoes develop a tough, white core in their center. The white tissue may appear in the area of the fruit just beneath the calyx or in the entire fruit.  The internal walls of the fruit may also appear pale in color and “corky.” Older tomato varieties may be more prone to this disorder. High heat and improper fertility seem to be related to its formation. Malnourished plants with poor foliage cover tend to bear fruit that is exposed to the sun, thus adding to the problem of temperature stress of the fruit.
Poor fruit set is mostly hindered by extremes in temperatures. It occurs when complete fertilization doesn’t occur. High temperatures, especially if accompanied by low humidity, hinder fruit set through failure of viable pollen to form and/or fertilization to occur. Daytime temperatures above 95°F and night-time temps above 70°F can result in poor flowering and less fruit.
Delay in ripening occurs when there is a deviation from the normal temperature range.  Extremely stressful temperatures can virtually halt the process entirely.  Color developments in tomatoes occur in the very final stages of ripening and are also temperature-sensitive. The red pigment lycopene and yellow pigment carotene are the two pigments that give a tomato fruit its color.
Yellow-shouldered fruit is a physiological disorder characterized by areas at the top (shoulder) of the fruit remaining yellow and as the remainder of the fruit ripens and turns red. These yellow areas never ripen properly and the tissue below them is tough and poorly flavored. Tomato varieties that are green shouldered when immature are more likely to show the trait than varieties that have uniformly-green immature fruit. It appears that both temperature and nutrition are involved in the development of yellow shoulder.
These are just a few of the issues you may run into while trying to grow that juicy red tomato, but they are not big enough problems to keep you from succeeding.  Remember to: choose proven varieties that have disease resistance, irrigate consistently, maintain a correct pH, and fertilize adequately, especially with nitrogen, calcium, and potassium. Follow these tips and you too can grow a beautiful, delicious tomato!

By:  Dr. Jeff Wilson

Dr. Jeff Wilson is a Regional Horticulture Specialist serving northeast Mississippi with Mississippi State University’s Extension Service. 
For more horticulture information, you can follow Dr. Wilson on Twitter @MSUPlantMan or email him at

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